1. Field of the Invention
The present invention is directed to an ophthalmic shunt for treating glaucoma by draining fluid from the anterior chamber of the eye.
2. Description of the Prior Art
Glaucoma is a blinding disorder caused by optic nerve damage resulting from elevated intraocular pressure. The elevated pressure is a direct result of the inability of the eye to drain the aqueous humor fluid from the anterior chamber of the eye, which is formed between the lens-iris plane and the cornea. Aqueous fluid is created by the ciliary body, and serves to provide nutrients for the lens and to carry away waste products resulting from the metabolism of the surrounding tissues. In a normal eye, the aqueous produced by the ciliary travels through the pupil into the anterior chamber, is removed through the trabecular meshwork, and passes through Schlemm's canal and into blood vessels. The balanced flow and removal of aqueous fluid to and from the anterior chamber allows for maintenance of a healthy intraocular pressure. However, if the necessary rate of outflow is not maintained, for example, due to an obstruction of the trabecular meshwork, fluid buildup in the anterior chamber occurs. This results in intraocular pressure elevation, and the optic nerve may be damaged.
Prior art devices for treating glaucoma include a variety of implants which allow aqueous fluid to flow from the anterior chamber, bypassing the trabecular meshwork, and thereby relieving the intraocular pressure. For example, U.S. Pat. No. 4,521,210 to Wong discloses an implant device shaped as a cruciform, including a main stem portion and an integral cross arm. The front end of the device has a sharp edge. The device is curved along its length so as to allow the device to lie against the interior surface of the sclera when implanted. The device is implanted by creating a scleral flap adjacent the ciliary body which is retracted to expose a scleral bed. Two incisions are made through the bed. The sharp-edged front end of the device is inserted into the forward incision to separate the sclera from the ciliary body, with the forward edge extending into the anterior chamber and disposed adjacent the inner layers of the cornea. The rearward edge is inserted into the suprachoroidal space between the sclera and choroid, and the scleral flap is sutured over the implant.
The device of Wong relieves pressure in the anterior chamber by allowing aqueous fluid to flow from the anterior chamber along the length of the implant and into the suprachoroidal space, where it is absorbed into the blood system. However, since Wong's device extends within the anterior chamber adjacent to the inner surfaces of the inner corneal layers, it may come into contact with the sensitive inner corneal layer, that is, the endothelium. Irritation of and possible damage to the endothelium may result. Further, Wong's device is disposed entirely within the eye, making the implantation thereof a relatively complicated procedure, and also making it impossible to control the rate of fluid flow from the anterior chamber to the suprachoroidal space after implantation.
U.S. Pat. No. 4,946,436 to Smith discloses an implant device which is placed in a pocket made in the sclera. The implant includes a porous interior. To insert the device, both an upper and lower flap of the sclera are raised into the cornea. The inner flap of sclera is then excised at the approximate location of the limbus, allowing access to the anterior chamber. The implant is disposed over the opening in the pocket created in the sclera by removal of the flaps, with the anterior portion of the device anchored in a lamellar shelf created in clear cornea.
In Smith, the aqueous fluid is carried to the sclera by the porous interior of the implant. No suprachoroidal space is created for receiving fluid flow since Smith's implant is not long enough to extend into the suprachoroidal space. Further, since the implant is made of a porous hydrogel material, it is not rigid enough to maintain such a space.